This section provides background information related to the present disclosure, which is not necessarily prior art.
Separation operations span across many manufacturing industries and account for annual energy consumption of 4,500 trillion BTU/year of energy, which is about a quarter of all in-plant energy use in the United States. Fuel separations account for a significant portion of this energy consumption. Equipment for power generation, motor vehicle operation, or reusable rocket operations often require liquid fuels that must meet strict chemical composition specifications in order to satisfy numerous safety, service lifetime, environmental, and regulatory criteria. For example, sulfur content in most liquid fuels used in the United States is tightly controlled in order to, among other reasons, enable the operation of emissions control equipment containing catalysts that are poisoned by sulfur compounds. In addition, many types of modern engines are sensitive to levels of aromatic or nitrogen-containing impurities in liquid fuels due to the build-up of solid residues on critical surfaces, which is believed to be highly accelerated in the presence of these impurities.
Some methods have been developed to remove impurities from fuel feedstock streams, such as hydrodesulfurization (“HDS”), which requires large scale chemical processing equipment for contacting multiple liquid phases, including distillation columns, high-pressure reaction vessels, or large vessels, all of which are highly energy intensive. Furthermore, in certain scenarios, such as after a major natural disaster, these large-scale refineries may be off-line or otherwise unable to provide the refined fuels, which are needed for operation of equipment (including emergency response vehicles and generators) for an extended period of time.
More recent technological advances in fuel refining have not yet been fully implemented into conventional practice for at least two reasons. First, many processes remove both sulfur and aromatic compounds; however, the aromatic content of fuels must often be preserved for compatibility with engine seals and other key system components. Second, large quantities of spent extract are often generated—whereas a highly mobile refinery must otherwise function by recycling at least a small quantity of initially supplied extractant.
As a result, there exists a continuing need for processes to economically, efficiently, and reliably remove impurities from feed streams, especially from liquid fuel feedstocks. This is especially difficult where the one or more impurities to be separated from the feed stream are miscible with the other components in the feed stream. The greatest opportunities for energy savings in separation of miscible components lie in replacing high-energy operations (e.g., distillation) with low-energy alternatives (e.g., extraction). In extraction, one of the primary design challenges is to maximize the interfacial area between the feed and the extractant for efficient mass transfer. This is typically accomplished by energy-intensive techniques such as ultrasonication or pumping the feed and the extractant through columns with moving internals or through packed columns with high tortuosity (which display high resistance to fluid flow). A relatively less energy-intensive technique, primarily used in microfluidic extraction, is emulsification of the feed and the extractant. While emulsions, especially those stabilized by surfactants, provide a large interfacial area and greatly enhance the mass transfer in extraction, the subsequent separation of the extract phase (typically the desirable phase) and the raffinate phase (typically the undesirable phase) can be energy-intensive and less economical.
Consequently, there is a great need and a significant opportunity to develop new energy-efficient extraction methodologies with enhanced mass transfer. There, thus, remains a need for simplified separations processes, including fuel refining processes, that are highly effective and energy efficient, thus not requiring large-scale chemical processing equipment, and that can be accomplished via mobile platforms.